1. Field of the Invention
The present invention relates to an optical fiber connector unit which, in an assembly process of an optical fiber connector to an optical fiber cord (hereinafter referred to as "assembly"), simplifies the assembly in an automatic assembly line, and is labor-saving with a manual assembly, and to an optical connector having the optical fiber connector unit.
2. Description of the Prior Art
In contrast to fusion splicing for permanently connecting optical fibers, an optical connector is a joining device capable of detachably connecting optical fibers with one another. Various types of optical connectors are known which can easily connect and disconnect optical fibers.
To promote further popularization of wide area information services including video information to individual homes and offices, an economical optical fiber connector is essential. Heretofore, optical fiber connectors were composed of a number of parts, which have been highly dependent on manual assembly processes. As a result, 50% of the total cost is accounted for by the assembly cost, which has impeded reducing the cost of the optical fiber connector. Therefore, in order to meet the needs for optical connectors in the future and provide an economical optical fiber connector, it is necessary to automate the assembly work, thereby improving the productivity and reducing the assembly cost.
To achieve an automatic assembly apparatus for optical fiber connector at a reasonable cost, it is necessary to simplify the mechanism and assembly process as much as possible for this purpose, it is preferable to reduce the number of components of the optical fiber connector and simplify the structure of the connector so that the assembly process can be simplified.
Optical fiber connectors that are presently used are broadly divided into a bayonet fastening type, such as an ST-type connector, and a push-pull fastening type, such as an SC-type connector.
The ST-type connector, which was developed by AT & T of the United States, has a structure in which a ferrule and a spring are preassembled with a bayonet coupling nut. The three parts (ferrule, spring, and coupling nut) are supplied in an integrated form.
FIGS. 1A to 1C are schematic views showing the connector structure and assembly procedure of the ST-type connector. As shown in FIGS. 1A to 1C, a ferrule 102 for holding an optical fiber 101a and an optical fiber strand 101b having a jacket is previously incorporated in a bayonet type coupling nut 104, together with a spring 103 to form a plug unit 105. The optical fiber cord 101 is retained to the ferrule 102 of the plug unit 105 using a crimp ring 106. A hood 107 for protecting the retained portion is engaged with the coupling nut 104, thus forming an optical fiber connector.
In assembling the ST-type optical fiber connector shown in FIG. 1A, after optical fiber cord 101 is inserted into hood 107 and crimp ring 106, a sheath of an end portion, a strand jacket of optical fiber strand 101b, and a primary coating are removed to expose the optical fiber 101a. A tension member 101c, such as an aromatic polyamide Kevlar.RTM., is cut and formed properly. Then, as shown in FIG. 1B, optical fiber 101a and optical fiber strand 101b are inserted into ferrule 102, which is filled with an adhesive, and fixed therein. Tension member 101c is put over a rear end of ferrule 102 and crimp ring 106 is engaged thereto. Crimp ring 106 subsequently crimped to retain it to the rear end of ferrule 102. Finally, as shown in FIG. 1C, hood 107 is engaged with coupling nut 104 to cover crimp ring 106.
Since the ST-type connector comprises three parts (ferrule 102, spring 103, and coupling nut 104), the assembly time can be reduced over other types of connectors. However, the St-type connector uses tension member 101c to resist against an external force applied to optical fiber cord 101,thus protecting optical fiber strand 101b. Since tension member 101c is retained directly to ferrule 102 a small gap is formed between the ferrule end faces, which may break optical signals. Furthermore, the ST-type connector may be directly affected by an eccentric error generated in the production of the ferrule and the optical fiber. That is, when ST-type connectors differing in eccentric direction are connected, a deviation occurs between cores of the abutted optical fibers in the ferrules, which increases insertion loss (the insertion loss is the largest in a worst case scenario where eccentric directions differ by 180 degrees).
An F04 type single-core optical fiber connector (JIS 5973, hereinafter referred to as "SC-type connector"), which solves the problems of open circuit and increases in insertion loss present in the St-type connector, has a floating mechanism in which the ferrule floats from a stopring. The SC-type connector incorporates a core eccentricity adjusting mechanism for adjusting eccentricity in itself. As a result, the SC-type connector is used worldwide as a high-precision and reliable optical communication connector.
FIG. 2A and FIG. 2B are schematic views showing a structure and an assembly process of the SC-type connector. As shown in FIGS. 2A and 2B, the SC-type connector has a ferrule 202, a spring 203, a stopring 204, a boot 205, a ring 206, and a crimp ring 207 assemblable with an optical fiber cord and using a plug frame 208 retained to the stopring 204.
Structures of stopring 204 and plug frame 208 will be described in detail.
FIG. 3A is a partly cutaway schematic front view showing stopring 204. FIG. 3B is a left side view of stopring 204. As shown in the FIGS. 3A and 3B, stopring 204 has protrusions 204a projecting in the radial direction at two positions opposing each other on the outer peripheral surface.
FIG. 4A is a schematic longitudinal sectional view of plug frame 208. FIG. 4B is a cross sectional view of plug frame 208 taken along line A--A, and FIG. 4C is a schematic front view of FIG. 4A. FIG. 4D is a schematic left side view of FIG. 4C, and FIG. 4E is a schematic right side view of FIG. 4C. As shown in FIGS. 4A to 4E, two positions opposing each other on the inner peripheral surface of plug frame 208 are provided with holes 208a where projections 204a of stopring 204 are inserted. An inner diameter D.sub.0 between holes 208a is set smaller than an outer diameter d.sub.0 (see FIG. 3) between projections 204a of stopring 204. Plug frame 208 has a cutout 208b extending from an opening end and in the axial direction cutout 208b is at a position rotated 90 degrees from the holes 208a in a peripheral direction to allow elastic deformation of plug frame 208 to open the opening.
With the opening of plug frame 208 opened, stopring 204 is inserted into the plug frame and, projection 204a inserted in hole 208a. An external force is removed, and plug frame 208 returns to its original position due to its elasticity, so that stopring 204 is retained through projection 204a to plug frame 208, as shown in FIGS. 5A and 5B.
In assembling the SC-type connector having stopring 204 and the frame 208, first, as shown in FIG. 2A, the optical fiber cord 201 is inserted into stopring 204, and through coil spring 203, along with boot 205, ring 206, and crimp ring 207. Optical fiber 201 is pretreated i.e., the sheath, jacket and the primary coating are removed so that optical fiber 201a, optical fiber strand 201b, and tension member 201c are exposed. Then, as shown in FIG. 2B, ferrule 202, which is separately supplied, is bonded to the tip of optical fiber cord 201. In this condition, the individual inserted parts are held with the insertion positions undetermined relative to the optical fiber cord 201.
Subsequently, a core adjusting step is performed for the ferrule, which is polished to a convex-curved surface. Specifically, to set the eccentric direction of plug frame 208 with respect to the center of ferrule 202, the ferrule 202 is positioned at a first rotational position so that flange cutout 202a and inner projection 208c (see FIG. 4E) are in line. Then, coil spring 203 and stopring 204 are released and the parts are assembled. At this point, stopring 204 is positioned at a second rotational position so that the two projections 204a, provided on the stopring 204, are engaged with holes 208a of plug frame 208, and inserted as shown in FIG. 6B. FIG. 7 shows relative positions in an assembled condition of optical fiber cord 201, stopring 204, spring 203, and ferrule 202. The assembly of these components is all performed manually.
With the condition shown in FIG. 6B, as shown in FIG. 2C, crimp ring 207 is crimped with tension member 201c inserted between stopring 204 and crimp ring 207 to retain the cord. Boot 205 is set in position. In this case, ring 206 is used to retain the sheath to the end of crimp ring 207; alternatively, an adhesive may be used in place of ring 206. Finally, the coupling device is assembled as shown in FIG. 2D. In the coupling condition, ferrule 202 is pressed toward the left direction in FIG. 2 by a spring force caused by coil spring 203. An end of ferrule 202 contacts with stopring 204, and is floatingly supported to stopring 204 through coil spring 203.
To automate the above-described assembly process of the conventional SC-type connector, insertion positions of the individual parts having the optical fiber cord 201 inserted there through must be exactly determined. However, when a large number of parts are inserted to a flexible object, such as optical fiber cord 201, it is very difficult to mechanically recognize the positions of the inserting parts, which has impeded automation of the assembly. Further, in manual assembly, a large number of parts must be handled, requiring tedious work. In particular, in a field assembly of an optical fiber connector to a LAN optical fiber cord in an intelligent building using optical fiber cord 201 as a communication medium, the number of parts handled in the field is increased, and the construction time is considerably increased.
Furthermore, in the core adjusting step, two positioning steps i.e., the first rotational positioning and the second rotational positioning have been required, making it difficult to automate the assembly work.